The website (Kaleme.com) says Ahmad Yazdanfar was arrested late Monday night and taken to an unknown location.

He has worked as Mr. Mousavi's chief bodyguard for more than two decades.

Hundreds of activists, including several of Mr. Mousavi's aides and political allies, have been arrested in a crackdown of the opposition following their rejection of President Mahmoud Ahmadinejad's re-election last year.

Iran's opposition accuses Mr. Ahmadinejad of rigging the presidential election last June to give himself a second term. The opposition insists Mr. Mousavi was the rightful winner.